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ESP32 EN pin pulled down

Posted: Thu Nov 07, 2019 10:58 pm
by Devenda
Hi,


Something strange is happening on my custom board featuring a ESP32-WROOM-32.
The EN pin is being pulled down (seemingly from the ESP32 itself), effectively preventing the ESP32 from booting.
This has not happened before and the board had functioned flawlessly in the past.

When tying EN directly to 3V3 (instead of using a pullup) the ESP32 boots and shows output on the serial bus.
When measuring EN <> GND for shorts (with a powered down board) it shows no connection (but had previously shown a short/low resistance).

Is it possible that the ESP32 pulls EN down (due to previously being damaged, a certain config setting the pin low,...)?

Strangely, another board had a similar issue with GPIO0, preventing flashing. After (destructively) removing the ESP32 and measuring the PCB (and ESP32) no shorts were found, I ruled this a broken ESP32-WROOM.

Other boards currently work fine.

Any pointers would be welcome, thanks in advance!

Re: ESP32 EN pin pulled down

Posted: Fri Nov 08, 2019 3:37 am
by WiFive
viewtopic.php?f=12&t=11552

It is possible you had a short or whisker on your pcb and running 3.3v rail through it burned it out and fixed it.

Re: ESP32 EN pin pulled down

Posted: Fri Nov 08, 2019 6:39 am
by Devenda
That's something I thought of too. But the problem persists. Strangely it worked fine before. The only thing I can think of is that something else went wrong, damaging the esp32 wroom internally, but again it boots fine, I'm just unable to program it again...

Re: ESP32 EN pin pulled down

Posted: Fri Nov 08, 2019 4:04 pm
by vonnieda
Do you have your power enable tied to your ESP enable, by chance?

I had a problem where I had power enable and ESP enable tied together. When the ESP is not powered fully, it will sink current on EN (and other signals). In my case, when I would turn on EN, as power started to come up the ESP would pull EN back down causing power to fail.

The solution in my case was to separate power and ESP enable, bring up power first, and then ESP enable a few ms later.

Jason

Re: ESP32 EN pin pulled down

Posted: Fri Nov 08, 2019 8:30 pm
by Devenda
vonnieda wrote:
Fri Nov 08, 2019 4:04 pm
Do you have your power enable tied to your ESP enable, by chance?

I had a problem where I had power enable and ESP enable tied together. When the ESP is not powered fully, it will sink current on EN (and other signals). In my case, when I would turn on EN, as power started to come up the ESP would pull EN back down causing power to fail.

The solution in my case was to separate power and ESP enable, bring up power first, and then ESP enable a few ms later.

Jason
Thanks for the hint, but the only things connected are the auto program transistor, a pull up and switch. Even without all those it still is being pulled down.

So the only other options are an internal issue in de esp wroom, or an issue on the PCB but I don't suspect the latter.